The invention relates to a process and a device for manufacturing segmented pressure-sensitive adhesive layers and applying the same to a substrate, involving the use of a reaction medium containing radiation-induced monomers and/or prepolymers of olefinically unsaturated compounds, and optionally the addition of a photoinitiator.
Segmented pressure-sensitive adhesive layers are widely used in practice, for example, in such pressure-sensitive adhesives which are required to be water- or gas-permeable. Also, in some cases, reducing the consumption of pressure-sensitive adhesive is a reason for the segmentation of a pressure-sensitive adhesive layer.
Furthermore, segmentation is required if small areas are stuck to substrates. Here, it is only the area to be adhered which is to be provided with a segment of the pressure-sensitive adhesive layer.
The processes for segmentation, punching, knife application, and screen printing are known above all. Among these, punching has the disadvantage of entailing large amounts of waste. Knife application only permits production of limited layer thicknesses, which also applies to screen printing. The latter moreover requires a considerable expenditure in terms of the provision of contours.
U.S. Pat. No. 5,344,681 describes a process for segmentation wherein pressure-sensitive adhesive segments are produced in recesses of a carrier material. This involves particular difficulties in connection with the removal of the segments from the recesses.
Starting from the aforementioned prior art, it is the object of the invention to provide a process and a device which enable the manufacture of segmented pressure-sensitive adhesive layers of any desired thickness and contour in an economical manner as well as in a manner which can be readily realized in technical terms, and which are suitable for mechanization with high output using comparatively uncomplicated devices.
To achieve this object in a process for manufacturing segmented pressure-sensitive adhesive layers and for applying the same to a substrate, using a reaction medium containing radiation-inducible polymers and/or prepolymers of olefinically unsaturated compounds under addition of photoinitiators, the following sequence of operational steps is proposed with the present invention:
that the reaction medium is kept ready in a metering and filling station under absence of oxygen,
that the empty templates are conveyed, preferably intermittently one after another, with a lower covering of their segment-defining opening put against the said templates, to a filling station wherein they are filled with a dosable amount of the reaction medium,
that the filled templates are passed in continuous conveyance below a UV section, whereby the reaction medium is solidified by means of radiation-induced reaction involving at least partial polymerisation,
that after removal of the lower covering, the reaction medium, which is then exposed on the upper side and the bottom side, is, during the further transport between an upper and a lower UV section, fully cured from above and from below by continued radiation-induced polymerisation reaction to form the finished pressure-sensitive adhesive layer,
that the template, containing the finished pressure-sensitive adhesive layer, is conveyed to a transfer station wherein the pressure-sensitive adhesive layer is pushed out of the template and is combined with a substrate,
that, optionally, the substrate which has been equipped with the pressure-sensitive adhesive layer is conveyed by a conveyor belt to a final-manufacturing station (not shown).
The process is suitable for economically and continuously manufacturing segmented pressure-sensitive adhesive layers of any desired thickness and contour in a manner which is comparatively uncomplicated and can be readily realized in technical terms. More particularly, the process is suitable for use in a fully-mechanized device.
One embodiment of the process provides that the thickness of the segmented pressure-sensitive adhesive layer is defined by the thickness of the template.
Furthermore it is provided by the invention that the template and the lower covering are rendered anti-adhesive, with the template and lower covering being made of dehesive material or the inner walls of the opening and the covering preferably being provided with a dehesive coating.
A further embodiment of the process provides that the polymerization reaction is performed by irradiating the reaction medium with ultraviolet light or electron radiation, and that the ultraviolet light is preferably generated by a laser.
The process is further characterized in that to produce the pressure-sensitive adhesive layer, acrylate-based pressure-sensitive adhesives are selected with preference, and that the mixture of monomers is principally employed under addition of a photoinitiator.
Also, a prepolymer may be used for polymerization. Since during polymerization, the reaction medium is subjected to a volume shrinkage, a corresponding embodiment of the process provides for the addition to the reaction medium of an additive compensating the volume shrinkage occurring in the course of polymerization.
Since the reaction medium must be protected from access of oxygen during its handling up to the time of performing the polymerization reaction, it has proved advantageous to render the environment of the template inert by means of nitrogen, in order to increase the degree of reaction. Since in the case that the reaction medium is metered into an opening of the template it is not absolutely necessary that said opening be filled-up completely, the thickness of the pressure-sensitive adhesive can be adjusted in accordance with the filling amount to be metered, i.e. the thickness can be smaller than the thickness of the template. As a consequence, in the manufacture of the adhesive layer it is possible to vary the thickness within relatively broad limits without the need of making a new template for each thickness.
A device for manufacturing segmented pressure-sensitive adhesive layers and applying the same to a substrate, more particularly for realizing the process according to the invention, is characterized by the following structural features:
a continuous conveyor belt or chain for templates to be conveyed in circulation,
a base or support belt running synchronously within the said conveyor belt, under section-wise formation of a lower covering,
a first, upper UV section and a subsequent lower UV section,
a transfer station comprising a template-emptying device.
As a transfer station, a turnstile is suitable.
In the vertical axis, a turnstile is mounted above the template to be emptied. From below, the contoured adhesive tape is pushed upwards out of the template by means of a plunger or punch. The turnstile consists of 4 arms fitted at a distance of 90xc2x0, each arm having a suction foot and a pneumatic cylinder.
A cycle starts at 0xc2x0 at the magazine (4), from which the suction device takes out the piece which is to be rendered self-adhesive. The arm is rotated through 90xc2x0 counter-clockwise and reaches a station (5) where the surface is processed (e.g. corona discharge pre-treatment). After a rotation of altogether 180xc2x0, at the push-out and transfer station (3) the piece is placed onto the template in exact position. With the aid of the push-out plunger provided at the bottom side, the piece, which has been rendered self-adhesive, is then jointly removed from the template. The said piece, after a further rotation of altogether 270xc2x0, is placed on a dehesive conveyor-belt (6) and is subsequently subjected to final manufacturing processes. After the final 90xc2x0 rotation, the cycle is repeated, respectively, started anew (360xc2x0=0xc2x0).
The device is comparatively uncomplicated and is suitable for mechanized, continuous production of segmented pressure-sensitive adhesive layers using uncomplicated technological means.
One embodiment of the device provides that the templates have openings to receive the reaction medium, said openings having unrestricted segment-defining geometric shapes.
Furthermore, an embodiment of the device may be characterized in that the base or support belt in parts has segment-shaped protuberances forming pressure-sensitive adhesive-free volume portions by projecting into openings of templates and preventing the filling thereof with reaction medium. These protuberances have been rendered dehesive. They offer the possibility of forming areas which are surrounded on all sides by pressure-sensitive adhesive. Finally, the device provides that the templates have a thickness of between 0.5 to 6 mm.
Further details, features and advantages of the invention will become apparent from the following explanation of an embodiment example which is schematically represented in the drawings. The device shown in the Figure comprises a continuous conveyor belt or chain 14 for templates 10 to be conveyed in circulation. These are attached, at pre-determined distances from each other, to the transport chain 14 and circulate clockwise according to arrow 19 about a respective pair of deflector rolls. Each of the said templates 10 has segment-defining openings 18 which are closed in the region of the filling station 1 at their bottom side by a support belt 15 under formation of a lower covering 11, so that at the filling station 1 the still liquid reaction medium can be filled in portions into each opening 18. The reference numeral 20 designates the filling amount in each template 10. The filling amount may take up only part of the thickness of the templatexe2x80x94as illustrated xe2x80x94but it may also from case to case fill up the template 10 in its full height. After a template 10 has been filled with reaction medium at the filling station 1, it runs in continuous transport initially under a UV section A, in a section 2 of the line, and subsequently thereto in a section 2xe2x80x2 of the line between an upper UV section A and a lower UV section B, with the reaction medium, which is then exposed at the upper side and the bottom side, being fully cured from above and from below by continued radiation-induced polymerisation reaction to form the finished pressure-sensitive adhesive layer 13.
At the intersection of the transport distances 2 and 2xe2x80x2 the support belt 15 had previously run off downwards, thus removing the lower covering 11, and thereby exposed the underside of the reaction medium for polymerization reaction from below.
Then the template 10 containing the finished pressure-sensitive adhesive layer 13 is conveyed to the transfer station 3, where the pressure-sensitive adhesive layer 13 is pushed out from the template 10 with the aid of a plunger- or punch-shaped emptying device 16, and is delivered to the transfer station 3.
In the transfer station 3, with the aid of the template-emptying device 16 the ready-polymerized pressure-sensitive adhesive layer 13 is delivered, after it has been pushed out of the template 10, to an arm of the conveyor means 17 configured as a turnstile, and is held therein, for example, by action of suction.
The turnstile 17 takes individual substrates 12 from a stock (not shown in detail) and delivers them to an arm, each arm being provided with a suction foot and compressed-air cylinder.
A cycle starts at 0xc2x0 rotation at the magazine or depot 4, from which the suction arm 21 removes the piece 12 which is to be rendered self-adhesive. The arm is then rotated through 90xc2x0 anti-clockwise and reaches station 5, where the surface of a piece 12 is processed, for example, by coronary pre-treatment. After a further rotation through altogether 180xc2x0, at transfer station 3 the piece 12 is placed in exact position on the template 10, whereafter, with the aid of the push-out plunger 16 provided at the bottom side, joint removal of the piece which has been rendered self-adhesive takes place.
Following a further rotation of the turnstile arm of altogether 270xc2x0, the said piece 12, together with the pressure-sensitive adhesive layer 13, is placed on a conveyor belt 6 which has been adjusted to be dehesive, and is subsequently subjected to final-manufacturing processes. After the final 90xc2x0 rotation, the cycle is completed and a new cycle of 360xc2x0 will be started.
The invention will be illustrated by means of the following examples.